This invention relates to thermally stable diamond compacts.
Abrasive compacts are well known in the art and are used extensively in industry for the abrading of various workpieces. They consist essentially of a mass of abrasive particles present in an amount of at least 70%, preferably 80 to 90%, by volume of the compact bonded into a hard conglomerate. Compacts are polycrystalline masses and can replace single large crystals. The abrasive particles of compacts are invariably ultra hard abrasives such as diamond and cubic boron nitride.
Abrasive compacts may contain a second phase or bonding matrix which contains a solvent (also known as a catalyst) useful in synthesising the particles. In the case of diamond, examples of suitable solvents are metals of group VIII of the periodic table such as cobalt, nickel or iron or an alloy containing such a metal. The presence of these solvents in diamond compacts renders them thermally sensitive at temperatures above 700.degree. C. In other words, at temperatures above 700.degree. C. degradation of the diamond is likely to occur. This, together with the differences in coefficients of thermal expansion of the diamond and solvent, causes structural degradation of the compact. The result is that the compact is substantially weakened or rendered useless as an abrasive.
U.S. Pat. No. 4,224,380 describes a method of leaching out a substantial quantity of solvent from a diamond compact. The resulting product is therefore substantially free of catalyst and is thermally more stable than the unleached product. Such a compact has an ability to withstand temperatures of up to 1200.degree. C. under vacuum without significant structural degradation of the compact occurring. The compact is known as a thermally stable compact.
Other thermally stable diamond compacts have been described in the literature and used commercially. For example European Patent Publication No. 0 116 403 describes a thermally stable diamond compact comprising a mass of diamond particles present in an amount of 80 to 90% by volume of the body and a second phase present in an amount of 10 to 20% by volume of the body, the mass of diamond particles containing substantial diamond-to-diamond bonding to form a coherent skeletal mass and the second phase containing nickel and silicon, the nickel being in the form of nickel and/or nickel silicide and the silicon being in the form of silicon, silicon carbide, and/or nickel silicide.
A further example of a thermally stable diamond compact is that described in the specification of British Patent Application No. 8508295. The thermally stable diamond compact comprises a mass of diamond particles present in an amount of 80 to 90 percent by volume of the compact and a second phase present in an amount of 10 to 20 percent by volume of the insert, the mass of diamond particles containing substantial diamond-to-diamond bonding to form a coherent skeletal mass and the second phase consisting essentially of silicon, the silicon being in the form of silicon and/or silicon carbide.
European Patent Publication No. 0 104 063 describes a method of bonding a cubic boron nitride compact to a cemented carbide support. The method includes the steps of metallising a surface of the cubic boron nitride compact by bonding a layer of gold, silver or a gold or silver-based alloy to that surface and bonding the metallised surface to a surface of the cemented carbide support through a braze alloy having a liquidus temperature above 700.degree. C. The preferred braze alloy contains at least 40 percent by weight silver, gold or a combination thereof, and 1 to 10 percent by weight of an active metal selected from the group of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium and molybdenum. The disclosure of the specification is specifically limited to the bonding of a cubic boron nitride compact to a cemented carbide support.
The disclosures of the four specifications mentioned above are incorporated herein by reference.